Introduction Bony bridge which develops between radius and ulna secondary to a specific event must differentiate from congenital radioulnar synostosis Epidemiology Incidence 3% to 9% Risk factors trauma related Monteggia fracture both bone forearm fractures at the same level open fracture, significant soft-tissue lesion comminuted fracture high energy fracture associated head trauma bone fragments on the interosseous membrane treatment related use of one incision for both radius and ulna delayed surgery > 2 weeks screws that penetrate interosseous membrane bone grafting into interosseous membrane prolonged immobilization Anatomy Forearm anatomy Presentation History previous trauma or surgery in forearm Symptoms pain with incomplete synostosis no pain with complete synostosis Physical exam pronation and supination blocked both actively and passively Imaging Radiographs recommended views AP and lateral of forearm, elbow, and wrist findings bony bridge between radius and ulna Treatment Operative surgical resection of synostosis, irradiation, and indomethacin indications mature post-traumatic synostosis that impairs function excision indicated at 4-6 months timing is controversial excision too early can lead to recurrence excision too late can lead to surrounding joint contractures results results of resection are poor except for midshaft synostosis proximal radial excision indications reserved for patients who have a proximal radioulnar synostosis that is too extensive to allow a safe resection, involves the articular surface, and is associated with an anatomic deformity. results can provide forearm rotation associated with radioulnar and/or elbow instability